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Galactic collision leaves glowing scar

By Richard Stenger

The blue arc, upper right, is a vestige of a violent merger between a dwarf star group and the larger galaxy Centaurus A, lower image.
The blue arc, upper right, is a vestige of a violent merger between a dwarf star group and the larger galaxy Centaurus A, lower image.

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(CNN) -- A large galaxy absorbed a smaller companion and left behind a bright blue imprint in the heavens that stretches thousands of light-years across, according to astronomers.

The long blue arc was produced in the wake of a cosmic merger that happened between 200 million and 400 million years ago, scientists said.

When the galaxy Centaurus A tore apart and ate its diminutive neighbor, it sparked the formation of thick bands of young blue stars, which account for the strange cosmic feature.

The Johns Hopkins University researchers had not intended to search for vestiges of dwarf galaxies when they spotted it in high-resolution telescope images.

"One of the joys of science is unexpected discoveries," said Holland Ford, one of the JHU astronomers, in a statement.

"Although our pictures were taken for another project, we decided to search the data for evidence of shredded dwarf galaxies. We were very excited when the blue arc popped out of one of the images."

Ford and colleagues, who announced their find this month, theorize that such cases of galactic gobbling contribute to the formation of halos on the outer boundaries of galaxies.

Such halos are astronomical artifacts, which can help scientists piece together cosmic events that shape galaxies over billions of years.

"Time scales for things to happen in halos are very long, which means they may preserve conditions that reveal how a galaxy formed and evolved," said Eric Peng, lead author of the report to be published in the December issue of the Astronomical Journal.

In the case of Centaurus A, an ellipse or elongated galaxy 10 million light-years away, there are signs that it collided with another large galaxy before consuming its tiny neighbor.

The cosmic feast could herald what happens in our galactic neighborhood several billion years from now.

"When our galaxy merges with the Andromeda Galaxy in the distant future, the Milky Way's satellite galaxies ... will likely be involved in that merger," Peng said.

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